The operation of electric machines such as generators is accompanied by the generation of heat particularly originating from so called copper losses in the stator. In order to provide proper cooling of a respective electric machine, it is known to blow a gaseous cooling medium from the face sides of the electric machine into the air gap between the stator and the rotor of a respective electric machine. The gaseous cooling medium circulates in axial direction, i.e. axially along the air gap, and in radial direction, i.e. through respective radial channels or ducts within the stator, through the electric machine.
Thereby, the axial flow velocity of the gaseous cooling medium is inversely proportional to the radial flow velocity of the gaseous cooling medium. Hence, due to the fact that the axial flow velocity of the gaseous cooling medium usually gradually decreases from the face sides to the centre of the generator or stator respectively, the radial flow velocity in the radial channels or ducts disposed in the regions of its face sides is usually lower in comparison to the radial flow velocity in the radial channels or ducts disposed in the centre portions of the generator or stator, respectively.
This effect gives rise to an uneven axial distribution of the radial flow velocity of the gaseous cooling medium within respective radial channels or ducts and hence, negatively affects the cooling efficiency of the generator as a whole.